1. Technical Field of the Invention
The present disclosure generally relates to conductive slurries for a solar battery and preparation methods thereof. More particularly, the present disclosure relates to aluminum back surface field slurries for a solar batteries and methods of preparing the same.
2. Description of the Related Art
More and more attention has been paid on solar power as a green energy nowadays. The conventional Si based solar battery is generally manufactured by: printing a conductive slurry containing a conductive metal powder, a glass powder and an organic carrier onto a Si substrate, then drying and burning the substrate to prepare an electrode. Generally, the front electrode of the Si substrate is a negative electrode, and the conductive slurry coated on the negative electrode is generally the Ag conductive slurry. The back electrode of the Si substrate is a positive electrode, and the conductive slurry coated on the positive electrode is the Al conductive slurry.
The aluminum conductive slurry has great effects on the performance of the solar battery. The research on the aluminum conductive slurry is mainly focused on the following aspects: (1) enhancing the photoelectric conversion efficiency; (2) after being sintered the Al film having a strong adhesive force to the Si substrate, without any Al globules or bubbles; (3) after being sintered the Al film not crooking or crooking as less as possible; and (4) Ensuring the performance of other components of the solar battery and the EVA film.
To solve the above mentioned problems, an aluminum back surface field conductive slurry for a solar battery as well as a method of preparing the same are proposed in the prior art. The method comprises steps of: adding a certain amount of functional elements such as gallium (Ga), indium (In), or thallium (Ti), etc. to the original lead borosilicate glass powder so as to remelt the mixture; adding rosin to the slurry to improve the conductivity of the Al film; using calcium stearate (or zinc stearate) as a lubricant to improve the screen-printing performance of the slurry; employing a surface coated with a 3-5 nm conductive metal powder; screen printing the aluminum slurry prepared above onto the crystalline silicon solar battery such that the sintered solar battery plate is less crooked without any aluminum globules. Also, while forming a Si—Al compound, no scar is formed, and the aluminum film is smooth; the average photoelectric conversion efficiency of the monocrystalline silicon battery is greater than 17.0%. Moreover, by adding functional elements such as Ga, In, or Ti, etc. the conductivity of the glass powder is enhanced. Meanwhile the linear expansion coefficient of the glass powder is changed, so that there are certain effects on enhancing the photoelectric conversion efficiency and reducing the crooking degree of the silicon plate after being sintered.
Meanwhile, a method of preparing an aluminum back surface field conductive slurry for a solar battery by synthesizing is proposed in the prior art. In this method, the prepared slurry comprises about 0.1-5.0 wt % of an In powder. The glass powder with or without lead is obtained by chemical method. The battery plate obtained by sintering the above slurry has a high photoelectric conversion efficiency and conductivity, and the coating has a strong adhesive force to the silicon substrate. The silicon plate has no or a little crook. The aluminum film has a smooth surface with no aluminum globules or bubbles.
However, the aluminum back surface field conductive slurry prepared according to the above method may leak through the screen while being placed onto the screen before being printed, which may affect disadvantageously the quality of the product, and result in agglomeration and sedimentation during storage, thus disadvantageously and seriously affecting the application of the conductive slurry.